> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 (current TTS) and Pulse (current
> STT). Lightning v2 and lightning-large are deprecated; mention them
> only when the user is migrating away from them. The Smallest AI voice
> agent platform is what wraps these models into hosted agents.

# Start an outbound call

POST https://api.smallest.ai/atoms/v1/conversation/outbound
Content-Type: application/json

Initiates an outbound telephony call with a specified agent and phone number.

## Caller-ID resolution

Every call names the number it dials from:

1. `fromNumber` present: resolved against the numbers your organization owns
   (rented numbers and outbound SIP trunk caller IDs). Must match **exactly** as
   stored, E.164 with the leading `+` and no spaces (`+14155552671`). An unowned
   or unmatched number returns `400` ("... is not one of your outbound numbers").
2. `fromNumber` omitted (**deprecated fallback**): the call dials from the
   agent's attached caller IDs (see `POST /agent/{agentId}/caller-ids`), first
   attached wins. This fallback is the compatibility bridge and sunsets with the
   migration window, after which `fromNumber` is required; calls that used it
   respond with a `Deprecation: true` header so you can find them in your logs.
   With no caller IDs attached, the call is refused with `400` ("No caller ID
   for this call — pass a number to dial from, or attach a caller ID to the
   agent"). Calls to numbers on the Do Not Call list are refused with `403`
   ("Call blocked: number is on Do Not Call list").

There is no silent fallback to a platform-owned number (dashboard test calls are
the only exception). `fromProductId` is still accepted as a legacy alias and is
resolved to its phone number first.

## Resolved-config check

The call uses the agent's currently-active version. If your most
recent prompt change went through `PATCH /workflow/{workflowId}` and
the agent has versioning enabled, that change may not have
propagated to the active version — and the call will play the
platform-default greeting instead of your prompt. Before placing a
production call, fetch `GET /agent/{agentId}` and confirm
`_resolvedConfig.firstMessage` (and related fields) match what you
intended. The
[Versioning Lifecycle](/atoms/developer-guide/build/agents/versioning-lifecycle)
guide covers the correct edit flow.

**400 is returned for:**

* Invalid `agentId` format (`"Invalid agent id"`)
* Invalid `phoneNumber` format (`"Invalid phone number"`)
* Invalid `fromProductId` format (`"Invalid product id"`)
* `fromNumber` that is not one of your rented numbers or outbound-trunk caller IDs (`"...is not one of your outbound numbers"`)
* `fromProductId` that does not resolve to an active number in your organization (`"Phone number not found or not active for your organization"`)
* No number to dial from: `fromNumber` omitted and the agent has no caller ID attached (`"No caller ID for this call — pass a number to dial from, or attach a caller ID to the agent"`)
* Agent not found or not in the caller's org (`"Agent not found"`)
* Agent is archived (`"Agent is archived and cannot initiate calls"`)
* `workflow_graph` agent has no workflow configured (`"Workflow not found"`)
* Workflow has validation errors (`"Invalid workflow, please fix the errors..."`)

**403** is returned for `workflow_graph` agents when the org lacks conversational agents access.

**Test calls:** set the `x-test-call: true` header to mark the resulting call log as a test call
(`isTest: true`). Test calls are subject to concurrent slot limits.

Reference: https://docs.smallest.ai/api-reference/voice-agents/calls/start-outbound-call

## Authentication

- `Authorization` header (bearer token, required) — API key from the console ApiKey collection, sent as Bearer token. Also accepts session cookies for browser-based auth.

## Request

### Headers

- `x-test-call` (enum, optional) — Set to "true" to mark this as a test call. The call log will have isTest=true and counts against concurrent test-call slot limits.
  - Allowed values: `true`

### Body (application/json)

This endpoint expects an object.

- `agentId` (string, required) — 24-character hex id of the agent initiating the conversation
- `phoneNumber` (string, required) — The E.164 phone number to call
- `variables` (map from string to ConversationOutboundPostRequestBodyContentApplicationJsonSchemaVariables, optional) — Variables to inject into the agent's prompt at call time. Values must be string, number, or boolean — nested objects are not supported.
- `fromNumber` (string, optional) — The caller ID to dial from, E.164 with the leading `+`, matched exactly against your rented numbers and outbound SIP trunk caller IDs (no normalization is applied; `+1 415 555 2671` or `14155552671` will not resolve). See "Caller-ID resolution" above for what happens when omitted.
- `versionId` (string, optional) — ID of a specific published agent version to use for this call. Useful for test calls — attributes the call log to that version so you can track which version was tested.
- `operatorId` (string, optional) — Integration operator identifier. Pass `"webengage"` to trigger the WebEngage integration flow.
- `operatorData` (map from string to any, optional) — Arbitrary data passed to the operator (e.g. `userId`, `journeyId` for WebEngage).
- `fromProductId` (string, optional, deprecated) — Legacy alias for `fromNumber`. The ID of a telephony product (phone number) to call from, resolved to its number before dialing. Prefer `fromNumber`.

## Response

### 200

Successfully started the outbound conversation

- `status` (boolean, optional)
- `data` (ConversationOutboundPostResponsesContentApplicationJsonSchemaData, optional)

## Errors

### 400 Bad Request Error

Invalid input

- `status` (boolean, optional)
- `errors` (list of string, optional)

### 401 Unauthorized Error

Unauthorized access

- `status` (boolean, optional)
- `errors` (list of string, optional)

### 403 Forbidden Error

Forbidden access

- `status` (boolean, optional)
- `data` (ApiResponseData, optional)

### 500 Internal Server Error

Internal server error

- `status` (boolean, optional)
- `errors` (list of string, optional)

## Types

### ConversationOutboundPostRequestBodyContentApplicationJsonSchemaVariables

### ConversationOutboundPostResponsesContentApplicationJsonSchemaData

- `conversationId` (string, optional) — The callId of the initiated call (format `CALL-{13-digit-timestamp}-{6-char-hex}`). Use this value as the `id` path parameter in `GET /conversation/{id}` and as an entry in `POST /conversation/search`.

### ApiResponseData

## Examples

**Request**

```json
{
  "agentId": "60d0fe4f5311236168a109ca",
  "phoneNumber": "+1234567890"
}
```

**Response**

```json
{
  "status": true,
  "data": {
    "conversationId": "CALL-1737000000000-abc123"
  }
}
```

**SDK Code**

```python
import requests

url = "https://api.smallest.ai/atoms/v1/conversation/outbound"

payload = {
    "agentId": "60d0fe4f5311236168a109ca",
    "phoneNumber": "+1234567890"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript
const url = 'https://api.smallest.ai/atoms/v1/conversation/outbound';
const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '{"agentId":"60d0fe4f5311236168a109ca","phoneNumber":"+1234567890"}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.smallest.ai/atoms/v1/conversation/outbound"

	payload := strings.NewReader("{\n  \"agentId\": \"60d0fe4f5311236168a109ca\",\n  \"phoneNumber\": \"+1234567890\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby
require 'uri'
require 'net/http'

url = URI("https://api.smallest.ai/atoms/v1/conversation/outbound")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"agentId\": \"60d0fe4f5311236168a109ca\",\n  \"phoneNumber\": \"+1234567890\"\n}"

response = http.request(request)
puts response.read_body
```

```java
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.smallest.ai/atoms/v1/conversation/outbound")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"agentId\": \"60d0fe4f5311236168a109ca\",\n  \"phoneNumber\": \"+1234567890\"\n}")
  .asString();
```

```php
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.smallest.ai/atoms/v1/conversation/outbound', [
  'body' => '{
  "agentId": "60d0fe4f5311236168a109ca",
  "phoneNumber": "+1234567890"
}',
  'headers' => [
    'Authorization' => 'Bearer <token>',
    'Content-Type' => 'application/json',
  ],
]);

echo $response->getBody();
```

```csharp
using RestSharp;

var client = new RestClient("https://api.smallest.ai/atoms/v1/conversation/outbound");
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Bearer <token>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"agentId\": \"60d0fe4f5311236168a109ca\",\n  \"phoneNumber\": \"+1234567890\"\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift
import Foundation

let headers = [
  "Authorization": "Bearer <token>",
  "Content-Type": "application/json"
]
let parameters = [
  "agentId": "60d0fe4f5311236168a109ca",
  "phoneNumber": "+1234567890"
] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api.smallest.ai/atoms/v1/conversation/outbound")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```